I’m trying to test a custom ACME server against certbot. I see that I can change the acme path using --server, but I haven’t been able to find the flag for changing the ca-bundle so that I can do server auth verification.

Yeah, I also couldn’t find anything in the docs. It’s an environment variable we pick up courtesy of the requests library, but we’ve used it before in Boulder testing. If you’re interested in filing an issue or a PR for the Certbot docs, I think that would be cool!